Mikhail Khrizanforov

Electrochemical properties of diphosphonate-bridged palladacycles and their reactivity in arene phosphonation

A series of diphosphonate-bridged dipalladacycles [(phpy)Pd(EtO)2P(O)]2, [(bhq)Pd(EtO)2P(O)]2, [(phpz)Pd(EtO)2P(O)]2 (phpy=2-phenylpyridine, bhq=benzo[h]quinoline, phpz=1-phenylpyrazole), which are known to be involved in catalytic C–H phosphonation reactions, was prepared and characterized by NMR spectroscopy and cyclic voltammetry in acetonitrile solutions and in carbon paste electrode. Diphosphonate dipalladacycles are oxidized irreversibly at more positive potentials as distinguished from related acetate palladacycles. Electrochemical preparative oxidations carried out under mild conditions without any specially added oxidants quantitatively afforded corresponding arylphosphonates. For complete conversion of dipalladacycles into arylphosphonates, four electrons per each palladium atom are required, that probably indicates a mechanism involving Pd(IV)/Pd(II) redox couple.

One-stage synthesis of FcP(O)(OC2H5)2 from ferrocene and α-hydroxyethylphosphonate

A new approach is proposed for ferrocene phosphorylation using α-hydroxylalkylphosphonate as a “masked” phosphorylating agent, by electrochemical reduction of a ferrocene and (Me)2C(OH)P(O)(OC2H5)2 mixture at −50 °C. The method makes it possible to obtain the product of diethyl ferrocenyl phosphonate with a high yield (87–89%) and 100% conversion of the initial phosphonate in one stage. It is evidenced with experiments that ferrocene reduction is carried out with preservation of the iron charge in the ferrocene fragment and with the formation of a cyclopentadienyl ligand radical anion at −3.3 V ref. Ag/AgCl (at −50 °C).

Electrochemical phosphorylation of coumarins catalyzed by transition metal complexes (Ni—Mn, Co—Mn)

A possibility of electrochemical phosphorylation of coumarins (coumarin, 6-methylcoumarin, 7-methylcoumarin) with diethyl phosphite was shown. The approach is based on the oxidation of a mixture of the aromatic compound and diethyl phosphite (1: 1) under mild conditions (room temperature, atmospheric pressure) in the presence of a bimetallic catalytic systems: MnIIbipy/NiIIbipy and MnIIbipy/CoIIbipy (bipy is the 2,2´-bipyridine). This method allows one to obtain diethyl arylphosphonates in high yields (up to 70%) and 100% conversion of the phosphite.

Electrochemical oxidative phosphonation of azoles

GRAPHICAL ABSTRACT ABSTRACT Metal-catalyzed electrochemical oxidative phosphonation of hetaryl-azoles (benzoxazoles, benzothiazole and others) with dialkyl-H-phosphonate was developed. Joint electrochemical oxidation of azoles and dialkyl-H-phosphonate mixtures in the presence of catalytic quantities of salts of transition metals at room temperature affords the desired 2-substituted azoles. Palladium, nickel and silver salts were tested as catalysts.

Eco-efficient electrocatalytic C–P bond formation

Abstract The development of practical, efficient and atom-economical methods of formation of carbon-phosphorus bonds remains a topic of considerable interest for the current synthetic organic chemistry and electrochemistry. This review summarizes selected topics from the recent publications with particular emphasis on phosphine and phosphine oxides formation from white phosphorus, chlorophosphines in electrocatalytic processes using aryl, hetaryl or perfluoroalkyl halides as reagents. This review includes selected highlights concerning recent progress in modification of catalytic systems for aromatic C–H bonds phosphonation involving metal-catalyzed ligand directed or metal-induced oxidative processes. Furthermore, a part of this review is devoted to phosphorylation of olefins with white phosphorus under reductive conditions in water-organic media. Finally, we have also documented recent advances in ferrocene C–H activation and phosphorylation.

Electrochemical pathway to CH/PH functionalization of diphenylphosphine oxide

GRAPHICAL ABSTRACT ABSTRACT Electrochemical oxidative CH/PH functionalization reaction between diphenylphosphine oxide and diphenylacetylene has been performed. The yield of target cyclisation product was obtained with 76% yield after 4F of electricity was passed through the reaction mixture at 1.0 V (vs. Ag/AgCl).

Electrooxidative CH/PH functionalization as a novel way to synthesize benzo[b]phosphole oxides mediated by catalytic amounts of silver acetate

Electrochemical joint oxidation of diphenylphosphine oxide with acetylenes in the presence of silver acetate (10%) as a catalyst yields benzo[b]phosphole oxide derivatives under mild conditions at room temperature without additional oxidants or initiators and with yields up to 100%. The redox properties of the key intermediate of the catalytic cycle have been investigated by cyclic voltammetry and EPR spectroscopy. The Ph2P(O)Ag intermediate oxidizes easier (+0.05 V vs. Fc+/Fc) than all reaction precursors to form the phosphinyl radical Ph2P(O)˙, fixed as a spin-adduct by ESR. Thus, a radical mechanism type through the Ag+/Ag0 couple was developed for electrocatalytic conditions.

Electrooxidative phosphorylation of coumarins by bimetallic catalytic systems Ni(II)/Mn(II) or Co(II)/Mn(II)

GRAPHICAL ABSTRACT ABSTRACT The phosphorylation of coumarins (coumarin, 6-methylcoumarin, 7-methylcoumarin) by catalytic oxidation of a mixture of coumarins and diethyl phosphite (1:1) in electrochemical mild conditions (room temperature and normal pressure) using bimetallic catalyst systems, MnCl2bpy/Ni(BF4)2bpy or MnCl2bpy/CoCl2bpy(bpy-2,2′-bipyridine) was realized.

Various ways of C-P bonds formation via selective electrochemical phosphorylation of aromatic C-H bonds

GRAPHICAL ABSTRACT ABSTRACT Principal achievements and modern trends in the development of new methods of electrocatalytic phosphorylation are analyzed and generalized. Possibilities and advantages of the electrochemical preparation of phosphorus compounds are demonstrated. The attention is focused on the CH-substitution of aromatic substrates by electrochemical reactions.

Novel phosphonium salt for paste electrode to study the redox properties of insoluble compounds

GRAPHICAL ABSTRACT ABSTRACT A new carbon paste electrode is described, which contains the room temperature ionic liquid tri(tert-butyl)(decyl)phosphonium tetrafluoroborate as a binder. The advantages of this electrode are a high conductivity, very wide electrochemical window (5.4 V from 2.7 V to −2.7 V, one of the widest ever reported for RTILs), stability in time, and reproducibility.